1. Field of the Invention
This invention relates to automatically inspecting matter, for example automatic inspection and sorting of discrete objects of differing compositions, e.g. waste objects, or automatic inspection of sheet material, which may be in the form of a strip, for surface layer composition, e.g. surface layer thickness.
With the recent focus on collection and recycling of waste, the cost effectiveness of waste sorting has become an essential economic parameter.
2. Description of Related Art
In the “Dual System” in Germany all recyclable “non-biological” packaging waste excluding glass containers and newsprint is collected and sorted in more than 300 sorting plants.
Objects can be sorted on the basis of:—                Size        Density/weight        Metal content (using eddy current effect)        Ferrous metal content (using magnetic separation)        
but most objects such as plastics bottles and beverage cartons are still today sorted out manually to a considerable extent. Some beverage cartons contain an aluminium barrier and by eddy current induction they can be expelled from the waste stream. Generally, beverage cartons in their simpler form present a composite object consisting of paperboard with polymer overcoats on both their inside and outside surfaces.
Several sorting systems exist today that can sort a number of different plastics bottles/objects from each other when they arrive sequentially (i.e. one-by-one). The detection is based on reflected infrared spectrum analysis. To separate the various polymers a quite elaborate variance analysis is performed and thus detection systems become expensive. The objects being fed sequentially pass beneath the infrared spectral detector whereby infrared is shone onto the objects and the relative intensities of selected wavelengths of the infrared radiation reflected are used to determine the particular plastics compound of the plastics passing beneath the detection head. Downstream of the detection head are a number of air jets which blow the individual plastics objects into respective bins depending upon the plastics which constitutes the majority of the object.
A similar system is disclosed in U.S. Pat. No. 5,134,291 in which, although the objects to be sorted can be made of any material, e.g. metals, paper, plastics or any combination thereof, it is critical that at least some of the objects be made predominantly from PET (polyethylene terephthalate) and PS (polystyrene) as well as predominantly from at least two of PVC (polyvinyl chloride), PE (polyethylene) and PP (polypropylene), for example objects including: an object made predominantly from PET, an object made predominantly from PS, an object made predominantly from PVC and an object made predominantly from PE. A source of NIR (Near Infra Red), preferably a tungsten lamp, radiates NIR onto a conveyor sequentially advancing the objects, which reflect the NIR into a detector in the form of a scanning grating NIR spectrometer or a diode array NIR spectrometer. The detector is connected to a digital computer connected to a series of solenoid valves controlling a row of air-actuated pushers arranged along the conveyor opposite a row of transverse conveyors. The diffuse reflectance of the irradiated objects in the NIR region is measured to identify the particular plastics of each object and the appropriate solenoid valve and thus pusher are operated to direct that object laterally from the conveyor onto the appropriate transverse conveyor. The computer can manipulate data in the form of discrete wavelength measurements and in the form of spectra. A measurement at one wavelength can be ratioed to a measurement at another wavelength. Preferably, however, the data is manipulated in the form of spectra and the spectra manipulated, by analogue signal processing and digital pattern recognition, to make the differences more apparent and the resulting identification more reliable.
DE-A-4312915 discloses the separation of plastics, particularly of plastics waste, into separate types, on the basis of the fact that some types of plastics have characteristic IR spectra. In the IR spectroscopic procedure, the intensity of diffusely reflected radiation from each sample is measured on a discrete number of NIR wavelengths simultaneously and the intensities measured are compared. Measurements are taken on wavelengths at which the respective types of plastics produce the minimum intensities of reflected radiation. If, for example, three different plastics are to be separated, each sample is measured on three wavelengths simultaneously, whereby one type of plastics is identified in a first comparison of the intensity of the reflected radiation on the lowest wavelength with that of the second-lowest wavelength and the other two types of plastic are determined in a second comparison of the greater intensity on one wavelength in the first comparison with the intensity on the third wavelength. To measure the light on particular wavelengths, respective detectors can have narrow band pass filters for the respective requisite wavelengths, and respective constituent cables of a split optical fibre cable are allocated to the respective detectors, the cable entry lying in the beam path of a lens for detecting the light reflected from the sample. Alternatively, a light dispersing element, e.g. a prism or grid, is placed in the beam path after the lens and several detectors are arranged to detect the NIR of the requisite wavelengths. Sorting facilities are controlled by utilising the detection data obtained by the comparisons. As a further example, five differing plastics, namely PA (polyamide), PE, PS, PP and PETP, may be separated, utilising measurement points at five differing wavelengths between 1500 nm. and 1800 nm.
EP-A-557738 discloses an automatic sorting method with substance-specific separation of differing plastics components, particularly from domestic and industrial waste. In the method, light is radiated onto the plastics components, or the plastics components are heated to above room temperature, light emitted by the plastics components and/or light allowed through them (in an embodiment in which light transmitted through the components and through a belt conveying them is measured) is received on selected IR wavelengths, and the material of the respective plastics components is identified from differences in intensity (contrast) between the light emitted and/or absorbed, measured on at least two differing wavelengths. The light emitted or allowed through is received by a camera which reproduces it on a detector through a lens. A one-dimensional line detector is usable, although a two-dimensional matrix detector or a one-element detector with a scanning facility can be employed. In order that the camera may receive the light on selected IR wavelengths, interference filters may be mounted either in front of the light source or in front of the lens or the detector. In an example in which the material of the plastics components is identified from the differences in intensity of emitted light at two differing wavelengths, the wavelengths are chosen to produce maximum contrast. This means that one wavelength is selected so that maximum intensity of the emitted light is obtained at a specified viewing angle, whereas the other wavelength is selected so that minimum intensity is obtained at that viewing angle. Changing of wavelengths may be achieved by mounting the filters on a rotating disc, with the frequency of rotation being synchronised with the imaging frequency of the detector. Alternatively, an electrically triggered, tunable, optical filter may be employed. The electrical signals generated by the detector are fed to an electronic signal processor, digitised, and subsequently evaluated by image processing software. It is ensured that the plastics components are at approximately the same temperature at the time of imaging, as differences in contrast can also be caused by temperature differences. The belt should consist of a material which guarantees constant contrast on individual wavelengths.
There is also previously known a system in which infrared spectral detection is performed from below the objects, with the objects passing sequentially over a hole up through which the IR is directed. Again, the infrared reflected is used to sort the objects according to the various plastics within the respective objects.
U.S. Pat. No. 5,260,576 and U.S. Pat. No. 5,339,962 disclose a method and apparatus for distinguishing and separating material items having different levels of absorption of penetrating electromagnetic radiation by utilising a source of radiation for irradiating an irradiation zone extending transversely of a feed path over which the material items are fed or passed. The irradiation zone includes a plurality of transversely spaced radiation detectors for receiving the radiation beams from the radiation source, the detectors receiving the radiation substantially on a direct line from the source. The material items pass through the irradiation zone between the radiation source and the detectors and the detectors measure one or more of the transmitted beams in each item passing through the irradiation zone to produce processing signals which are analysed by signal analysers to produce signals for actuating a separator device in order to discharge the irradiated items toward different locations depending upon the level of radiation absorption in each of the items. The disclosure states that mixtures containing metals, plastics, textiles, paper and/or other such waste materials can be separated since penetrating electromagnetic radiation typically passes through the items of different materials to differing degrees, examples given being the separation of aluminium beverage cans from mixtures containing such cans and plastic containers and the separation of chlorinated plastics from a municipal solid waste mixture. The source of penetrating radiation may be an X-ray source, a microwave source, a radioactive substance which emits gamma rays, or a source of UV energy, IR energy or visible light. One example of material items which are disclosed as having been successfully separated are recyclable plastic containers, such as polyester containers and polyvinyl chloride PVC) containers, which were separated using X-rays. WO-A-95/03139 discloses a similar system which is employed for automatically sorting post-consumer glass and plastics containers by colour.
In an eddy current system for ejecting metal from a stream of waste, the discharge end roller of a belt conveyor normally contains a strong alternating magnetic field generated by permanent magnets contained within and distributed along the roller and counter-rotating relative to the sense of rotation of the roller. This field ejects metallic objects to varying degrees depending upon the amount and the conductivity of the metal of the object. Since metallic objects in which the metal content is small, for example post-consumer packaging cartons of a laminate consisting of polymer-coated paperboard and aluminium foil, are only weakly affected by the magnetic field, such cartons tend not to be separated-out by the eddy-current ejection system.
Another known system uses an electromagnetic field for eddy current detection through induction of eddy currents in the metal in metallic objects and the detection output is used to control an air jet ejection arrangement but this time the objects are caused to queue up one after another in single lines.
WO-A-96/06689 discloses a system for automatically inspecting matter for varying composition and comprising one or more detection stations through which one or more streams of matter are advanced and particular materials therein are detected through their diffusely reflected IR spectra, if any, and/or through their variation of an electromagnetic field by their metallic portions, if any. In one version, a multiplicity of detection points represented by lenses are distributed in a straight line across and below the stream as it passes over a transverse slot through a downwardly inclined plate at the downstream end of a conveyor belt, with a separate light source for each lens. Optical fibres transmit the IR from the respective lenses to a rotary scanner whence a diffuser shines the IR onto infrared filters ahead of IR detectors dedicated to respective wavelengths, to date output of which is utilised in controlling air jet nozzles which separate-out desired portions of the stream. In other versions, a row of light sources distributed across the overall width of one or more belt conveyors may cause desired portions of the stream at detection points distributed in an arc across the stream to reflect light diffusely onto a part-toroidal mirror extending over that overall width, whence the light is reflected, by a rotating, polygonal mirror through optical filters dedicated to differing IR wavelengths, onto detectors the data output of which is utilised in controlling solenoid valves operating air jet nozzles which separate-out the desired portions. Alternatively or additionally, an oscillator and an antenna which extends over that overall width generate an electromagnetic field through the belt and sensing coils sense variations therein produced by metallic portions of the stream passing through the detection station and the detection data produced by the sensing coils is used to control the solenoid valves operating the nozzles to separate-out the metallic portions. In a further version, the rotating, polygonal mirrors are retained and the part-toroidal mirror may be replaced by a mirror comprised of a series of facets or very small mirrors in a horizontal row transverse to the stream, which in this version is a laminate comprised of paperboard onto which a polymer has been extruded. The detection points are arranged in a straight row across the laminate.
JP-A-11-183399 describes a surface-flaw inspection device equipped with multiple camera units arranged one after another widthwise of matter to be inspected, in the form of a zinc-alloy-plated steel plate. Each camera unit incorporates at least two light-receiving cameras which observe the plate under differing optical conditions. The device also includes a processing section which determines the presence or absence of a surface flaw at each position in the width direction of the plate, based on the observation data received from the cameras incorporated in the corresponding camera unit. If the processing section is unable to obtain from a particular camera unit the observation data under all of the required optical conditions, at the boundary between the observation ranges of that camera unit and an adjacent camera unit, it uses the observation data obtained by that adjacent camera unit as the missing observation data to determine the presence or absence of a surface flaw at the boundary. The plate is illuminated by a linear diffusion light source which extends the entire width of the advancing plate. The light shines on to the plate from the light source at, for example, 60° to the vertical, through a cylindrical lens and a deflection board, the deflection angle of which is 45°. The light reflected from the plate travels directly to a mirror and thence to the camera units, which are fixed above the mirror.
CA-A-1219933 discloses the testing a sheet of transparent material, particularly flat glass, for flaws such as foreign substances or gas bubbles trapped in the sheet, in which the sheet is scanned with a flying light spot over its width, and the transmitted and reflected radiation is intercepted, converted into electrical signals, and evaluated. Above the sheet is a receiver for reflected radiation, while below the sheet is a receiver for transmitted radiation, the two receivers being connected to an evaluation unit, which is also connected to photomultipliers facing respective lateral edges of the sheet. In a preferred version, a laser is provided with a beam splitter which reflects a reference partial beam and another partial beam on to a rotary polygonal mirror having its axis substantially parallel to the direction of advance of the sheet. Because of the rotation of the mirror, the partial beams scan the entire width of the sheet, the reference beam being passed over a notched reference strip extending across the sheet. A photoelectric converter is assigned to each of the ends of the reference strip, receives light emerging from the reference strip and passes a corresponding signal to the evaluation unit. If the sheet contains a flaw in the form of a core bubble, the other partial beam no longer reaches the upper receiver but is deflected to the lateral edge face of the sheet, where it enters one or both of the photomultipliers. The reference beam scans the reference strip and enters it at its notches, pulses being produced in the relevant photoconverter(s) by the notches, these pulses being compared in the evaluation unit with corresponding values obtained from the photomultipliers.
U.S. Pat. No. 5,305,894 describes a system for sorting items, such as potato crisps, which computes the geometric centre of any item containing one or more defects and directs an ejection air blast at the geometric centre of the item. Video data from a scanning camera are transmitted to an item processor and a defect processor. The item processor builds in memory an image of every item, whether acceptable or defective, while the defect processor builds a defect list of defect coordinate locations detected only on defective items. The defect processor transmits the defect list to the item processor where the defect list is compared with the stored image of the item. For each defective item, the item processor computes its geometric centre that is added to a defective items list for use by a removal process that actuates air blasts directed towards the centres of defective items. The items may be brought to the removal station by a conveyor which projects the acceptable items on to another conveyor, whilst the air blasts direct downwards the defective items flying across the gap between the two conveyors.
U.S. Pat. No. 5,448,359 discloses an optical distance sensor according to the confocal optical imaging principle for the determination of height values and three-dimensional surface measurement, particularly in the inspection of complex units, for example equipped, printed circuit boards. An illumination beam from a laser passes through a coupling-out mirror on to a rotary polygonal mirror and thence through a scanning objective to the unit being inspected. The illumination beam is reflected from the unit back through the scanning objective and via the polygonal mirror to the coupling-out mirror whence it passes through a beam splitting unit as partial beams on to a plurality of photodetectors. The height level within the depth of focus is recognisable by the photodetector with the greatest light intensity.
U.S. Pat. No. 4,996,440 discloses a system for measuring one or a plurality of regions of an object to be able to determine one or a plurality of dimensions of the object. In one example, the system utilises a mirror arrangement for transmitting pulsed laser light so that the light impinges downwards upon the object and for receiving the upwardly reflected light. The system includes a laser, a rotating planar mirror and a concave frusto-conical mirror encircling the planar mirror, which serve for directing the light beam towards the object. The frusto-conical mirror, the planar mirror and a light receiver serve for receiving light beams which are reflected from the object. Electronic circuitry connected to the light receiver serves for calculating the travel time of the beam to and from the object, with a modulator causing the light beam to be modulated with a fixed frequency and the rotating planar mirror and the frusto-conical mirror causing the light beam to sweep across the object at a defined angle/defined angles relative to a fixed plane of reference during the entire sweeping operation.
EP-A-0747665 describes detection of leading and trailing edges of objects advancing along a defined path. A light source directs a light beam toward a beamspot on the path. Light reflected from the beamspot is received by two light detectors. A leading edge of an advancing object approaching the beamspot substantially blocks the light from being received from one detector and, subsequently, a trailing edge of the object departing from the beamspot substantially blocks the light from being received by the other detector. Electrical circuitry is provided for distinguishing the changes in reflected light received at each detector and determining whether the leading edge or the trailing edge is blocking the reflected light. The data obtained are processed to provide information about the object, such as the height of the leading and trailing edges of the object and the length of the object.
JP-A-61-82106 discloses as conventional a method of detecting unevenness of a road surface from a slowly moving detection vehicle. The vehicle carries a vertically downwardly directed camera for capturing the road surface image and a projector shining light obliquely onto the road surface directly beneath the camera. It describes as its own invention having, instead of the single projector, a pair of projectors at respectively the left- and right-hand sides of the vehicle. The two projectors shine differently coloured light onto the road surface directly under the camera and the illuminated road surface is captured on camera in colour either continuously or at regular intervals. This facilitates distinguishing unevenness of the road surface from cracks therein.
U.S. Pat. No. 5,220,450 discloses a scanning optical system including a gas laser for emitting a writing beam, a rotary polygonal mirror for deflecting and reflecting the rays of light from the gas laser, a scanning lens that is telecentric with respect to an image plane and which focuses the deflected rays of light to form an image on the plane, a focus detector that receives the reflected light from the image plane to detect the state of focusing on the plane by the scanning lens, and a focus adjusting unit that brings the scanning lens into focus on the image plane on the basis of the output of the focus detector.